Flow rate regulating valve of hydraulic pump

ABSTRACT

A flow control valve for a hydraulic pump is disclosed, which is so constructed that a first pilot chamber (101A) and a second pilot chamber (101B) are arranged in a manner to face a piston (102), resulting in the piston (102) varying initial load of a spring (9). Constrictions (106A) and (106B) are arranged in the middle of a communication passage through which the second pilot chamber (101B) is drained and in the middle of a communication passage which permits the second pilot chamber (101B) to communicate with the first pilot chamber (101A), respectively.

TECHNICAL FIELD

This invention relates to a flow control valve for a hydraulic pumpsuitable for use as a hydraulic power source for a power steering deviceof a vehicle.

BACKGROUND ART

A power steering device equipped with a conventional flow control valvefor a hydraulic pump is disclosed in Japanese Patent Application No.115052/1995 filed by the assignee.

FIG. 7(A) shows a hydraulic pump in which a flow control valve FVdisclosed in the Japanese application is integrally incorporated. A vanepump VP is used as the hydraulic pump.

The vane pump VP includes a housing H constructed of a pump body 10 anda cover 11. The housing H is formed with a shaft hole 12, in which ashaft 14 is rotatably supported through a bearing 13 arranged in theshaft hole 12. The shaft 14 functions as a drive shaft for a rotor 15arranged in the pump body 10. The rotor 15 has a plurality of vanes 16radially incorporated therein.

Also, the rotor 15 is mounted thereon with a cam ring 17 as shown inFIG. 7(B) which is viewed along line X--X of FIG. 7(A). The cam ring 17has an inner surface formed into an elliptic shape. Driving of the shaft14 permits rotation of the rotor 15, during which the vanes 16 areaccessed to the inner surface of the cam ring 17. Thus, the vanes 16 arerotated while being intimately contacted with the cam ring 17 and permitchambers independent from each other to be defined therebetween.

When the chambers thus defined each are subject to a contraction stroke,hydraulic oil or fluid is discharged from a discharge port; whereas wheneach of the chambers is subject to an expansion stroke, hydraulic fluidis sucked thereinto.

The rotor 15 and cam ring 17 are commonly provided on a side surfacethereof with a side plate 18. This results in a high-pressure chamber 19being defined on a rear surface side of the side plate 18, so that apump discharge pressure may be guided to the high-pressure chamber 19. Apressure of hydraulic fluid in the high-pressure chamber 19 forces theside plate 18 against the rotor 15 to keep loading balance.

The flow control valve VP, which will be described hereinafter, isarranged in a manner to be integral with the pump body 10 of the vanepump VP, so that a body of the flow control valve VP may also act as thebody 10 of the vane pump VP.

The shaft 14 of the vane pump VP is connected to an engine (not shown),so that starting of the engine permits rotation of the rotor 15connected to the shaft 14. Thus, an increase in rotational speed of theengine leads to an increase in fluid discharge rate at which hydraulicfluid is discharged from the vane pump VP.

The hydraulic fluid thus discharged from the vane pump VP, as shown inFIGS. 4 to 6, is guided through a pump port 4 to a pressure chamber 8aof the flow control valve PV and fed from an actuator port 20a to apower steering circuit PS through a feed passage.

At this time, such flowing of the hydraulic fluid discharged results ina pressure difference occurring between both sides of a variableconstriction 3 arranged in the course or middle of the feed passage. Apressure on an upstream side acts on a left end surface of a spool 7positioned on a side of the pressure chamber 8a and a pressure on adownstream side acts on a right end surface of the spool positioned on aside of a pilot chamber 8b through a pilot passage 29.

However, the spool 7 is not permitted to be moved in a right-handdirection unless thrust obtained by multiplying the pressure differencebetween both sides of the variable constriction 3 by a pressurereceiving area of the spool 7 exceeds initial load of a spring 9 orunless a predetermined fluid discharge rate of the pump is obtained,resulting in a pump port 4 and a drain port 5 being kept isolated fromeach other. Therefore, all hydraulic fluid discharged from the pump isfed to the power steering circuit PS (an interval a of a characteristicline K shown in FIG. 4(B)).

When a rotational speed of the engine is increased to increase a fluiddischarge rate, resulting in the pressure difference between both sidesof the variable constriction 3 being increased to a predetermined levelor above, the spool 7 is moved in a right-hand direction against thespring 9. Then, the spool 7 is stopped at a position at which the thrustdescribed above and elastic force of the spring 9 are balanced with eachother, to thereby permit the pump port 4 and drain port 5 to communicatewith each other at a degree of opening corresponding to the position.This causes hydraulic fluid discharged from the pump to be returnedthereto through the drain pump 5 depending on the degree of opening, sothat the hydraulic fluid may be fed toward the power steering circuit PSat a maximum feed rate Q1 kept constant.

The maximum feed rate Q1 may be set on the basis of maximum powerassisting force required.

A further increase in engine speed or rotational speed of the enginecauses a decrease in fluid feed rate Q at which hydraulic fluid is fedto the power steering circuit PS for reasons described hereinafter. Moreparticularly, an increase in fluid discharge rate of the pump causes afurther increase in pressure difference between both sides of thevariable constriction 3, leading to further movement of the spool 7 inthe right-hand direction. Such movement of the spool 7 causes a diameterincreased section 23a of a constriction member 23 to forcedly enter aconstriction hole or orifice 22b, so that a degree of opening of thevariable constriction 3 may be reduced. Also, the constriction member 23is different in constriction effect thereof between when the diameterincreased section 23a partially enter the orifice 22b and when theformer entirely enters the latter. More specifically, an increase indegree at which the diameter increased section 23a enters the orifice22b increases a pressure difference between both sides of the variableconstriction 3, so that movement of the spool 7 may be increased toincrease a degree of opening of the variable constriction 3 whichaffects a degree of communication between the pump port 4 and the drainport 5.

Thus, as indicated by the interval b of the characteristic line K inFIG. 4(B), hydraulic fluid is fed toward the power steering circuit PSat the maximum feed rate Q1 kept substantially constant until arotational speed of the engine or an engine speed N reaches apredetermined level; whereas when the engine speed N exceeds thepredetermined level, a flow rate at which fluid is fed to the powersteering circuit PS is decreased, to thereby reduce the power steeringforce.

The engine speed N is substantially proportional to a velocity of thevehicle, to thereby permit application of the power assisting forcecorresponding to the velocity.

A maximum pressure applied to the power steering circuit PS isdetermined by a relief valve. More specifically, an increase in loadpressure in the power steering circuit PS leads to an abnormal increasein pressure in the first pilot chamber 8b, which then acts on a ballpoppet 33. When the pressure exceeds a relief set pressure determined bya spring 32, it forcibly opens the ball poppet 33 to permit the firstpilot chamber 8b and drain port 5 to communicate with each other.

Such communication between the pilot chamber 8b and the drain port 5causes fluid to flow through a pressure sensing hole 24, resulting in apressure loss occurring through the hole 24. This leads to an abruptreduction in pressure in the pilot chamber 8b, to thereby cause thespool 7 to be moved in a right-hand direction as shown in FIG. 5,resulting in a degree of opening of each of the pump port 4 and drainport 5 being increased to reduce a rate at which the pump feedshydraulic fluid or a fluid feed rate of the pump.

Then, when a pressure in the power steering circuit PS is reduced to alevel below the relief set pressure, the ball poppet 33 is set on avalve seat 34, so that a maximum pressure in the power steering circuitPS may be kept constant.

Also, the flow control valve FV, as shown in FIGS. 4 to 6, is soconstructed that a piston 35 is arranged opposite to the spool 7 and hasa change-over spool 36 incorporated therein.

Further, in the flow control valve FV, the spool 7 and piston 35 arearranged opposite to each other in the first pilot chamber 8b connectedthrough the pilot passage 29 to a downstream side of the variableconstriction 3 with the spring being interposedly arranged therebetween.This permits the piston 35 to be abutted against the spring 9 in thefirst pilot chamber 8b.

The piston 35 described above is formed on a central portion thereofwith a flange 37, which functions to partition a cylinder hole 50 into asecond pilot chamber 38 and a drain chamber 39. The drain chamber 39 isformed therein with a stepped portion 39a acting as a stopper, againstwhich the flange 37 is abutted to prevent further movement of the piston35.

The second pilot chamber 38 is arranged opposite to the first pilotchamber 8b with the piston 35 being interposed therebetween. Also, thedrain chamber 39 is permitted to communicate with a tank passage (notshown) and kept from communicating with the first pilot chamber 8b. Thepiston 35 has one pressure receiving surface 35a arranged so as to facethe first pilot chamber 8b and the other pressure surface 35b facing thesecond pilot chamber 38 and including a pressure receiving surface ofthe flange 37. The second pressure receiving surface 35b is formed so asto have a pressure receiving area larger than that of the first pressurereceiving surface 35a.

The piston 35 is formed therein with a spool hole 40 in a manner toextend in an axial direction thereof. The spool hole 40 is so arrangedthat one end or a left end thereof is open to the first pilot chamber 8band the other end or a right end thereof is closed. The spool thusformed has the change-over spool 36 slidably inserted thereinto, so thata pressure in the first pilot chamber 8b acts on a left end surface ofthe change-over spool 36.

Further, the spool hole 40 of the piston 35 is formed therein with anannular groove 41, which is arranged so as to communicate with thesecond pilot chamber 38 via a passage hole 42 of piston 35.

The change-over spool 36, as shown in FIG. 5(B), is formed thereon withtwo lands 43 and 44 in such a manner that an annular recess 45 isarranged therebetween. The right-hand land 44 of the change-over spool36 has elastic force of a spring 46 applied thereto.

The annular recess 45 is arranged so as to constantly communicate withthe drain chamber 39 through a passage 47 irrespective of a position ofthe piston 35 moved. Also, the change-over spool 36 is formed with acommunication hole 48, to thereby permit a chamber in which a spring 49is received to communicate with the drain chamber 39 through the annularrecess 45. The change-over spool 36 constructed as described above is sooperated that the land 43 interrupts communication between the firstpilot chamber 8b and the annular groove 41 and permits the second pilotchamber 38 to communicate with the drain chamber 39 through the annularrecess 45 and passage 47, when the change-over spool 36 is at a normalposition shown in FIG. 5(A).

When the pump 1 is actuated, hydraulic fluid discharged from the pump 1,as described above, is guided through the pump port 4 to the pressurechamber 8a, as well as through the variable constriction 3 to the powersteering circuit PS.

During non-steering, the power steering circuit PS is kept neutral, sothat the hydraulic fluid is returned to the tank, resulting in a loadpressure in the power steering circuit PS or a pressure on thedownstream side of the variable constriction 3 being reduced. This keepsthe pressure from exceeding a pressure set by the spring 46, so that thepiston 35 is maintained at the normal position shown in FIG. 5(A). Thisresults in initial load of the spring 9 in the first pilot chamber 8bbeing kept at a relatively reduced level.

Thus, the spool 7 is moved in the right-hand direction, until thrustobtained by multiplying a pressure difference between the pressurechamber 8a and the first pilot chamber 8b by a pressure receiving areaof the spool 7 overcomes elastic force of the spring 9 in the firstpilot chamber 8b, resulting in the spool 7 being balanced with load ofthe spring 9. Such movement of the spool 7 permits the pump port 4 tocommunicate with the drain port 5, so that the amount of fluid fed tothe power steering circuit PS is reduced correspondingly.

When a maximum feed rate Q2 during the non-steering is set to be lessthan the above-described maximum feed rate Q1, energy loss during thenon-steering requiring no assisting force may be significantly reduced.

During steering, when a pressure in the first pilot chamber 8b exceedsthe set pressure determined by the spring 46, the change-over spool 36is moved in the right-hand direction against elastic force of the spring46, to thereby permit the first pilot chamber 8b and annular groove 41to communicate with each other. The annular groove 41, as describedabove, is kept communicating with second pilot chamber 38 through thepassage hole 42, resulting in communication between the first pilotchamber 8b and the second pilot chamber 38. This permits a pressure onthe downstream side of the variable constriction 3 to be applied to eachof the first pilot chamber 8b and second pilot chamber 38. Suchapplication of the pressure on the downstream side of the variableconstriction 3 to both pilot chambers 8b and 38 causes the piston 35 tobe moved in the left-hand direction due to a difference in pressurereceiving area between the pressure receiving surfaces 35a and 35b ofthe piston 35 as shown in FIG. 6(A). The maximum amount of movement ofthe piston 35 is regulated by abutment between the piston 35 and thestopper or stepped portion 39a.

Such movement of the piston 35 forcibly compresses the spring 9,resulting in load of the spring 9 being relatively increased. Such anincrease in load of the spring 9 relatively reduces the amount ofmovement of the spool 7 which causes thrust based on a differencebetween a pressure in the pressure chamber 8a and that in the firstpilot chamber 8b to be balanced with load of the spring 9, so that theamount of fluid fed from the pressure chamber 8a to the drain port 5 maybe decreased. This results in a fluid feed rate at which fluid is fed tothe power steering circuit PS being increased to the maximum feed rateQ1, so that flow characteristics indicated at the characteristic line Kin FIG. 4(B) are obtained during the steering.

As will be noted from the above, the conventional flow control valve isso constructed that during the steering, the maximum feed rate Q1 isensured to provide the power steering circuit PS with sufficient powerand during the non-steering requiring no assisting force, the maximumfeed rate Q2 of the pump 1 is reduced as compared with the maximum feedrate Q1 ensured in the steering, to thereby minimize energy loss.

In the prior art described above, when the operation is changed from thenon-steering state to the steering state, a pressure in the first pilotchamber 8b is increased to cause the change-over spool 36 to be moved inthe right-hand direction against the spring 46, resulting in the firstpilot chamber 8b and second pilot chamber 38 communicating with eachother.

However, at this time, the left end surface of the change-over spool 36is caused to be open directly to the annular groove 41, so that thepassage thereof is rapidly increased in area. This causes thechange-over piston 35 to be rapidly moved in the left-hand direction,resulting in a feed pressure under which fluid is fed to the powersteering circuit PS or power assisting force being abruptly varied, sothat a driver of the vehicle has a feeling of disorder.

When the operation is changed from the steering state to thenon-steering state, the passage between the second pilot chamber 38 andthe first pilot chamber 8b is rapidly closed, followed by opening of thesecond pilot chamber 38 to the drain chamber 39, resulting in suchproblems as described above likewise occurring.

Also, in the prior art described above, the piston 35 is incorporateddirectly in a cylinder hole 50 formed in the body 10, followed byclosing of the cylinder hole 50 with a plug 51. This requiresincorporation of the piston 35 in the flow control valve duringassembling thereof, resulting in the assembling being highly troublesomeand costly. Further, for example, when it is desired to eliminate thepiston 35 from the flow control valve after incorporation of the piston35 into the flow control valve, it is required to remove the plug 51 andthen eliminate the piston 35 therefrom. Thus, such elimination of thepiston 35 is highly troublesome.

Moreover, in the prior art described above, the sleeve 49 pressedlyfitted in the body 10 and the spool 7 guided into the body 10 areinserted into the body 10 from a side of the pressure chamber 8a. Inorder to ensure a space required for the insertion, it is required toarrange a constriction plate 22 formed with the constriction hole ororifice 22b separately from the constriction member 23. Thus, it isrequired to threadedly hold the constriction plate 22 indirectly in thebody 10 by means of the plug 20 after incorporation of the sleeve 49 andspool 7 in the body 10.

Unfortunately, arrangement of the constriction plate 22 separately fromthe constriction member 23 causes misregistration between theconstriction member 23 of the spool 7 and the orifice 22b, to therebyfail to provide the constriction member 23 and orifice with satisfactorycoaxiality. This adversely affects a constriction effect or function ofthe variable constriction 3 constituted by a combination of the orifice22b and constriction member 23.

The present invention has been made in view of the foregoingdisadvantage of the prior art. It is an object of the present inventionto provide a flow control valve for a hydraulic pump which is capable ofkeeping a driver from having a feeling of any disorder when it is usedfor a power steering apparatus, constructing a piston into acartridge-type structure to facilitate incorporation thereof in the flowcontrol valve, and permitting a variable constriction to exhibit astable constriction function.

DISCLOSURE OF INVENTION

In accordance with one aspect of the present invention, a flow controlvalve for a hydraulic pump is provided. The flow control valve generallyincludes a variable constriction arranged in the middle of a hydraulicfluid feed passage for feeding hydraulic fluid discharged from ahydraulic pump, a body, a spool slidably incorporated in the body, apressure chamber arranged so as to face one end of the spool, a drainport arranged so as to communicate with a tank, a first pilot chamberarranged so as to face the other end of the spool, a spring arranged soas to act initial load on the end of the spool facing the first pilotchamber. The pressure chamber has a pressure on an upstream side of thevariable constriction guided thereto. The first pilot chamber has apressure on a downstream side of the variable constriction guidedthereto. The pressure chamber has a pressure therein which overcomeselastic force of the spring and an action of a pressure in the firstpilot chamber to move the spool when a pressure difference between bothsides of the variable constriction reaches a predetermined level ormore. Also, the pressure chamber is rendered open to the drain port at adegree of opening corresponding to a position of the spool. The flowcontrol valve also includes a piston arranged so as to face the firstpilot chamber while being opposite to the other end of the spool andabutted against the spring, a second pilot chamber arranged opposite tothe first pilot chamber with the piston being interposed therebetween,and a change-over spool slidably incorporated in the piston to permit apressure in the first pilot chamber to act thereon. The change-overspool acts to drain the second pilot chamber at a normal positionthereof and moving to permit the second pilot chamber to communicatewith the first pilot chamber when a pressure in the first pilot chamberreaches a predetermined level or more. The piston is so formed that afirst pressure receiving surface thereof facing the first pilot chamberhas an area smaller than that of a second pressure receiving surfacethereof facing the second pilot chamber.

The flow control valve according to the first aspect of the presentinvention thus generally constructed is characterized in thatconstrictions are arranged in the middle of a communication passagethrough which the second pilot chamber is drained and in the middle of acommunication passage which permits the second pilot chamber tocommunicate with the first pilot chamber, respectively.

In accordance with a second aspect of the present invention, a flowcontrol valve for a hydraulic pump is provided. The flow control valvelikewise includes a variable constriction arranged in the middle of ahydraulic fluid feed passage for feeding hydraulic fluid discharged froma hydraulic pump, a body, a spool slidably incorporated in the body, apressure chamber arranged so as to face one end of the spool, a drainport arranged so as to communicate with a tank, a first pilot chamberarranged so as to face the other end of the spool, a spring arranged soas to act initial load on the end of the spool facing the first pilotchamber. The pressure chamber has a pressure on an upstream side of thevariable constriction guided thereto. The first pilot chamber has apressure on a downstream side of the variable constriction guidedthereto. The pressure chamber has a pressure therein which overcomeselastic force of the spring and an action of a pressure in the firstpilot chamber to move the spool when a pressure difference between bothsides of the variable constriction reaches a predetermined level ormore. Also, the pressure chamber is rendered open to the drain port at adegree of opening corresponding to a position of the spool. The flowcontrol valve also includes a piston arranged so as to face the firstpilot chamber while being opposite to the other end of the spool andabutted against the spring, a second pilot chamber arranged opposite tothe first pilot chamber with the piston being interposed therebetween,and a change-over spool slidably incorporated in the piston to permit apressure in the first pilot chamber to act thereon. The change-overspool acts to drain the second pilot chamber at a normal positionthereof and moving to permit the second pilot chamber to communicatewith the first pilot chamber when a pressure in the first pilot chamberreaches a predetermined level or more. The piston is so formed that afirst pressure receiving surface thereof facing the first pilot chamberhas an area smaller than that of a second pressure receiving surfacethereof facing the second pilot chamber.

The flow control valve according to the second aspect of the presentinvention thus generally constructed is characterized in that the bodyis formed on an end thereof positioned on a side thereof opposite to thepressure chamber with a mounting port in a manner to face the other endof the spool, the change-over spool is incorporated in a piston and thesecond pilot chamber is previously formed in a piston casing, the pistoncasing is mounted in the mounting port together with the spring, so thatthe first pilot chamber is formed in a manner to face the spool andpiston, the spring is interposedly arranged between the spool and thepiston, and the piston casing is arranged so as to be detachable withrespect to the mounting port.

In a preferred embodiment of the present invention, the variableconstriction is constituted by a rod-like constriction member providedon the end of the spool facing the pressure chamber and a constrictionhole in which the constriction member is inserted. Also, the variableconstriction is so constructed that a degree of opening thereof isvaried depending on a relative position between the constriction memberand the constriction hole. The constriction hole is formed in aconstriction plate, which is integrally formed in the body.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing an embodiment of a flow control valvefor a hydraulic pump according to the present invention which is duringnon-steering;

FIG. 2 a sectional view of the flow control valve shown in FIG. 1 whichis during steering;

FIG. 3 is a sectional view of the flow control valve shown in FIGS. 1and 2 wherein a plug is substituted for a piston casing;

FIG. 4(A) is a circuit diagram showing a conventional power steeringdevice;

FIG. 4(B) is a graphical representation showing feed ratecharacteristics of the power steering device shown in FIG. 4(A);

FIG. 5(A) is a sectional view showing a conventional flow control valvewhich is during interruption of a pump;

FIG. 5(B) is a fragmentary enlarged sectional view showing a pistonincorporated in the flow control valve of FIG. 5(A);

FIG. 6(A) is a sectional view showing a conventional flow control valvewhich is during steering;

FIG. 6(B) is a fragmentary enlarged sectional view showing a pistonincorporated in the flow control valve of FIG. 6(A);

FIG. 7(A) is a sectional view showing a vane pump; and

FIG. 7(B) is an end view viewed along line X--X of FIG. 7(A).

BEST MODES FOR CARRYING OUT INVENTION

Referring first to FIGS. 1 to 3, an embodiment of a flow control valvefor a hydraulic pump according to the present invention is illustrated.A flow control valve of the illustrated embodiment is basicallyconstructed in substantially the same manner as the prior art describedabove; therefore, the following description will be made mainly inconnection with a structure of the illustrated embodiment different fromthe prior art. Also, detailed description of like components will beeliminated in principle.

The flow control valve of the illustrated embodiment is featured in thata change-over spool 106 is provided with constrictions 106A and 106B.

The illustrated embodiment is so constructed that during non-steering, aload pressure in a power steering circuit PS or a pressure on adownstream side of a variable constriction 3 is kept from exceeding aset pressure determined by a spring 105 as in the prior art describedabove. Thus, the piston 102 is kept at a normal position shown in FIG.1, at which a second pilot chamber 101B is permitted to communicate witha drain chamber 101C through a communication hole 102C, an annulargroove 102B, a passage hole 111B, a spring chamber 112 and a passage102A which are formed at the change-over spool 106. The constriction106B is arranged in the course or middle of such a communicationpassage. In the illustrated embodiment, the constriction 106B is formedby means of a drill or the like so as to extend in a directionperpendicular to an axial direction of the change-over spool 106.

Thus, when the piston 102 is at the normal position, a spring 9 hasinitial load kept at a relatively reduced level; so that a maximum feedrate Q2 may be reduced as compared with a maximum feed rate Q1 tominimize energy loss during non-steering requiring no assisting force asin the prior art described above.

Then, when the operation is changed over from the non-steering state toa steering state, a pressure in a first pilot chamber 101A is increasedwith an increase in load pressure in the power steering circuit PS, tothereby permit the change-over spool 106 to be moved against the spring105 as in the prior art described above. This, as shown in FIG. 2,permits the second pilot chamber 101B to communicate with the firstpilot chamber 110a through the communication hole 101C, the annulargroove 102B and a passage hole 11A, so that the piston 102 may be movedin a direction of contracting the spring 9 due to a difference inpressure receiving area between pressure receiving surfaces 102D and102E thereof. The constriction 106A is arranged in the middle of such acommunication passage. In the illustrated embodiment, the constriction106A is formed by means of a drill or the like so as to extend in adirection perpendicular to an axial direction of the change-over spool106.

Such movement of the piston in the direction in which the spring 9 iscontracted permits initial load of the spring 9 to be relativelyincreased, to thereby ensure the maximum feed rate Q1 required forproviding assisting force, resulting in preventing a shortage ordeficiency of power.

In the operation described above, the constriction 106A restricts anarea of the passage through which the first pilot chamber 101A andsecond pilot chamber 101B communicate with each other when the operationis changed over from the non-steering state to the steering state. Thispermits the piston 102 to be slowly moved during changing-over from thenon-steering state to the steering state, to thereby prevent a suddenvariation in feed pressure under which fluid is fed to the powersteering circuit PS or power assisting force, resulting in a driver fromhaving a feeling of any disorder.

Also, even when any pulsation occurs in the pressure in the first pilotchamber 101A, the constriction 106A absorbs or buffers such pulsation,to thereby keep it from being transmitted directly to the second pilotchamber 101B. This prevents any vibration of the piston 102 due to suchpulsation.

Arrangement of the constrictions 106A and 106B in the change-over spool106 in a manner to extend perpendicularly to the axis of the spool 106facilitates formation of the constrictions 106A and 106B, to therebyreduce a cost for the spool while ensuring the above-describedadvantage.

Further, in the illustrated embodiment, the piston 102 is incorporatedin a piston casing 101 rather than a body 10.

More specifically, the piston casing 101 is formed with a through-hole113 extending in an axial direction thereof, in which the piston 102 isslidably incorporated. The piston 102 is formed thereon with a flange114, which partitions the through-hole 113 into the second pilot chamber101B and drain chamber 101C described above. The drain chamber 101C isformed therein with a stepped portion 101D acting as a stopper, so thatthe piston 102 is kept from being further moved due to abutment thereofagainst the stepped portion or stopper 101D.

The through-hole 113 has a stopper 103 fitted in one end or a distal endthereof, which is securely held therein by means of a C-shaped pin 104.This permits the second pilot chamber 101B to be defined between thestopper 103 and the flange 114.

The drain chamber 101C is isolated from the first pilot chamber 101A bymeans of a seal 109. The drain chamber 101C is open through acommunication passage 101F to an outer peripheral surface of the pistoncasing 101.

The piston casing 101 thus formed is threadedly fitted in a mountingport 115 formed at one end of the body 10. At this time, thecommunication passage 101F communicating with the drain chamber 101C ispermitted to communicate with a tank passage (not shown) through achamber 100G defined by cooperation of the body 10 and piston casing 101with each other. Also, the piston casing 101 is formed in the other endor a distal end thereof with the first pilot chamber 101A whichconstitutes a part of the through-hole 113 and has the spring 9 arrangedtherein and in which a spool 7 is partially placed.

The above-described construction of the illustrated embodiment whereinthe piston 102 is previously incorporated in the piston casing 101 toprovide a cartridge structure facilitates incorporation of the piston102 in the flow control valve and reduces a manufacturing cost of thevalve.

Also, when a plug 117 adapted to be threadedly fitted in the mountingport 115 is provided separately from the piston casing 101 as shown inFIG. 3, any one of the piston casing 101 and plug 117 may be selectivelyincorporated therein as desired. This permits a user to select eitherthe flow control valve including the piston 102 or that free from thepiston 102 as desired.

In addition, the illustrated embodiment is so constructed that aconstriction hole or orifice 22b which constitutes a part of thevariable constriction 3 is formed in a constriction plate 116 integrallyprovided in the body 10 rather than in any constriction plate providedseparately from the body 10.

More particularly, the body 10 is provided therein with the mountingport 115, which is formed into a diameter larger than that of the spool7, so that the spool 7 may be inserted through the mounting port 115into the body 10. This eliminates a necessity of providing any spacerequired for insertion of the spool 7 on a side of the pressure chamber8a, therefore, it is not required to provide the constriction plate 116separately from the body 10.

Further, a spool hole 100E for slidably guiding the spool 7 therein andthe constriction hole 22b are directly formed in the body 10, so thatcoaxial formation thereof may be facilitated by means of a single chuck,to thereby provide both holes 100E and 22b with increased coaxiality.This permits coaxiality between a constriction member 23 provided in thespool 23 and the constriction hole 22b formed in the constriction plate116 to be necessarily increased, so that the variable constriction 3provided by a combination of both may exhibit a stable constrictionfunction.

The illustrated embodiment is free from any sleeve for slidably guidingthe spool 7. Alternatively, such a sleeve may be inserted into the body10. In this instance, the sleeve may be inserted thereinto from a sideof the mounting port 115.

INDUSTRIAL APPLICABILITY

The first aspect of the present invention permits initial load of thespring to be varied by the piston. Such construction of the presentinvention, when the flow control valve of the present invention is usedfor, for example, a power steering device, effectively preventsdeficiency of power on a side of the power steering circuit during thesteering and reduces the maximum feed rate of the pump to minimizeenergy loss during the non-steering.

In particular, arrangement of the constriction in the flow control valveof the present invention permits slow movement of the piston at the timewhen the first pilot chamber and second pilot chamber communicate witheach other and at the time when the communication therebetween isinterrupted. Thus, application of the flow control valve to the powersteering device prevents a sudden variation in fluid feed pressure tothe power steering circuit or power assisting force, to thereby keep adriver from having a feeling of any disorder.

Also, the flow control valve of the present invention, even when apressure in the first pilot chamber pulsates when the second pilotchamber is kept communicating with the first pilot chamber, permits theconstriction to buffer such pulsation of the pressure, to therebyprevent transmission of the pulsation directly to the second pilotchamber. This prevents vibration of the piston due to the pulsation.

The second aspect of the present invention permits the piston to beconstructed into a cartridge structure by previously incorporating thepiston in the piston casing, to thereby facilitate incorporation of thepiston in the body, resulting in reducing a manufacturing cost of theflow control valve.

When the plug adapted to be detachably mounted in the mounting port isprepared separately from the piston casing, it is possible to select thepiston casing or plug, to thereby provide either a piston-incorporatedflow control valve or a piston-free flow control valve as desired.

Further, in accordance with the present invention, the constrictionformed with the constriction hole may be integrally provided in thebody, so that the constriction hole may be formed coaxially with thespool hole. This permits coaxiality between the constriction hole andthe constriction hole of the spool guided in the spool hole to benecessarily increased, so that the variable constriction constructed ofa combination of both may exhibit stable constriction function.

We claim:
 1. A flow control valve for a hydraulic pump, comprising:avariable constriction (3) arranged in the middle of a hydraulic fluidfeed passage for feeding hydraulic fluid discharged from a hydraulicpump (VP); a body (10); a spool (7) slidably incorporated in the body(10); a pressure chamber (8a) arranged so as to face one end of thespool (7); a drain port (5) arranged so as to communicate with a tank; afirst pilot chamber (101A) arranged so as to face the other end of thespool (7); a spring (9) arranged so as to act initial load on the end ofthe spool (7) facing the first pilot chamber (101A); the pressurechamber (8a) having a pressure on an upstream side of said variableconstriction (3) guided thereto; the first pilot chamber (101A) having apressure on a downstream side of said variable constriction (3) guidedthereto; the pressure chamber (8a) having a pressure therein whichovercomes elastic force of the spring (9) and an action of a pressure inthe first pilot chamber to move the spool (7) when a pressure differencebetween both sides of the variable constriction (3) reaches apredetermined level or more; the pressure chamber (8a) being renderedopen to the drain port (5) at a degree of opening corresponding to aposition of the spool (7); a piston (102) arranged so as to face thefirst pilot chamber (101A) while being opposite to the other end of thespool (7) and abutted against said spring (9); a second pilot chamber(101B) arranged opposite to the first pilot chamber (101A) with thepiston (102) being interposed therebetween; and a change-over spool(106) slidably incorporated in the piston (102) to permit a pressure inthe first pilot chamber (101A) to act thereon; the change-over spool(106) draining the second pilot chamber (101B) at a normal positionthereof and moving to permit the second pilot chamber (101B) tocommunicate with the first pilot chamber (101A) when a pressure in thefirst pilot chamber (101A) reaches a predetermined level or more; thepiston (102) being so formed that a first pressure receiving surfacethereof facing the first pilot chamber (101A) has an area smaller thanthat of a second pressure receiving surface thereof facing the secondpilot chamber (101B), characterized in that:constrictions (106A) and(106B) are arranged in the middle of a communication passage throughwhich the second pilot chamber (101B) is drained and in the middle of acommunication passage which permits said second pilot chamber (101B) tocommunicate with the first pilot chamber (101A), respectively.
 2. A flowcontrol valve for a hydraulic pump, comprising:a variable constriction(3) arranged in the middle of a hydraulic fluid feed passage for feedinghydraulic fluid discharged from a hydraulic pump (VP); a body (10); aspool (7) slidably incorporated in the body (10); a pressure chamber(8a) arranged so as to face one end of the spool (7); a drain port (5)arranged so as to communicate with a tank; a first pilot chamber (101A)arranged so as to face the other end of the spool (7); a spring (9)arranged so as to act initial load on the end of the spool (7) facingthe first pilot chamber (101A); the pressure chamber (8a) having apressure on an upstream side of said variable constriction (3) guidedthereto; the first pilot chamber (101A) having a pressure on adownstream side of said variable constriction (3) guided thereto; thepressure chamber (8a) having a pressure therein which overcomes elasticforce of the spring (9) and an action of a pressure in the first pilotchamber to move the spool (7) when a pressure difference between bothsides of the variable constriction (3) reaches a predetermined level ormore; the pressure chamber (8a) being rendered open to the drain port(5) at a degree of opening corresponding to a position of the spool (7);a piston (102) arranged so as to face the first pilot chamber (101A)while being opposite to the other end of the spool (7) and abuttedagainst said spring (9); a second pilot chamber (101B) arranged oppositeto the first pilot chamber (101A) with the piston (102) being interposedtherebetween; and a change-over spool (106) slidably incorporated in thepiston (102) to permit a pressure in the first pilot chamber (101A) toact thereon; the change-over spool (106) draining the second pilotchamber (101B) at a normal position thereof and moving to permit thesecond pilot chamber (101B) to communicate with the first pilot chamber(101A) when a pressure in the first pilot chamber (101A) reaches apredetermined level or more; the piston (102) being so formed that afirst pressure receiving surface thereof facing the first pilot chamber(101A) has an area smaller than that of a second pressure receivingsurface thereof facing the second pilot chamber (101B), characterized inthat:the body (10) is formed on an end thereof positioned on a sidethereof opposite to the pressure chamber (8a) with a mounting port (115)in a manner to face the other end of the spool (7); the change-overspool (106) is incorporated in a piston (102) and the second pilotchamber (101B) is previously formed in a piston casing (101); the pistoncasing (101) is mounted in said mounting port (115) together with thespring (9), so that the first pilot chamber (101A) is formed in a mannerto face the spool (7) and piston (102); the spring (9) is interposedlyarranged between the spool (7) and the piston (102); and the pistoncasing (101) is arranged so as to be detachable with respect to themounting port (115).
 3. A flow control valve for a hydraulic pump asdefined in claim 1, characterized in that the variable constriction (3)is constituted by a rod-like constriction member (23) provided on theend of the spool (7) facing the pressure chamber (8a) and a constrictionhole (22b) in which the constriction member (23) is inserted;saidvariable constriction (3) is so constructed that a degree of openingthereof is varied depending on a relative position between theconstriction member (23) and the constriction hole (22b); and saidconstriction hole (22b) is formed in a constriction plate (116), whichis integrally formed in the body (10).
 4. A flow control valve for ahydraulic pump as defined in claim 2, characterized in that the variableconstriction (3) is constituted by a rod-like constriction member (23)provided on the end of the spool (7) facing the pressure chamber (8a)and a constriction hole (22b) in which the constriction member (23) isinserted;said variable constriction (3) is so constructed that a degreeof opening thereof is varied depending on a relative position betweenthe constriction member (23) and the constriction hole (22b); and saidconstriction hole (22b) is formed in a constriction plate (116), whichis integrally formed in the body (10).